The present invention refers to a quick coupling pipe fitting that is provided with a safety valve and a pressure relieve valve. In the transmission of fluids it is often necessary to avail of fitting that can be coupled rapidly to connect flexible or rigid pipes, connected themselves to a fluid feed and to users.
The known quick coupling fittings are generally composed of two elements, male and female, attached to corresponding pipes to be connected and coupled to each other by screw or trip means.
According to a currently known technique the female element is made of a structure comprising an interior body with one end inserted in an internally threaded nut for coupling with a feed or users and an exterior body coaxial to said interior body.
The interior body holds a valve element consisting of a fixed axial internal shaft with an enlarged end. Outside of this, concentrically, is coupled, in a way as to leave an interspace connectable afterwards to a feed or to users, a tightness bush that, under the elastic action of a positioning spring and through the engagement of the enlarged end of the shaft, closes tightly frontally said interspace with respect to the passage of fluid in absence of coupling with the male element.
Concentrically and externally to the bush, there is a cleaning unit of said bush composed of a sliding sleeve with its respective positioning spring.
An annular element with spokes is attached to the interior body, between the same and a back portion of the axial shaft, in which annular element a few small diameter holes are created for the passage of fluid. As an alternative, in order to avoid the turbulence associated with the presence of the small diameter holes, such annular element can be provided with at least two passage openings of annular sector shape following one another, spaced by narrow spokes, along the circumference of said annular element.
The male element generally comprises an exterior body provided with means for coupling with the female element on one end, an interior body coaxialiy fixed to said exterior body and an internally threaded nut fixed to the opposite end of said interior body for coupling of the male element to a feed or to users. Within said interior body an axial cavity is defined that is connectable afterwards to a feed or to users and that is closed frontally with a piston stressed by a positioning spring to a position of peripheral engagement with a seal held by the fore end of the interior body.
During coupling between the male element and the female element, the sliding sleeve of the female element is pushed by the interior body of the male element and, during its translation, draws with itself the bush against the strain force of its positioning spring. At the same time the inner axial shaft of the female element forces the piston of the male element to back against the force of the respective positioning spring up to a position of opening the inner cavity of the male element with the consequent definition of a passage opening for the fluid from a feed to users through the fitting. The bush of the female element is positioned at that moment within the seal of the male element in order to guarantee the side tightness of said opening.
If a fitting of this type is used at very high operating fluid pressures it may occur that at the moment of coupling the male element is under pressure and the female element is exhaust. Within the fitting there can be developed such high pressure difference as to compromise the stay of the internal seals in their seating. This occurs, in particular, with said seal of the male element; indeed, since the seating of the seal is usually rather spaced away from the fore end of the male element, it can occur that the seal remains uncovered and exposed to the fluid flow under pressure during the axial translation effected by the piston of the male element to engage with the bush of the female element, especially if the difference in pressure causes a displacement of the bush in an opposite direction. Due to the strong difference in pressure, the seal is subject to such stress as to be moved from its sealing. The consequent lack of tightness causes blow-by and fluid leakage from the fitting.
In order to avoid this inconvenience, in a known fitting described in EP-A-0686800 the male element includes also a safety valve located upstreanm of said male element cavity in the direction of fluid feed to said male element in order to close the communication between said feed and said cavity in the initial phases of coupling of the two elements of the fitting and to open instead said communication substantially at the end of said coupling.
In addition the male element seal is housed in a seating located very close to the fore end of the male element, so that said seal is covered by said bush of the female element in any axial position taken by said bush during said initial and final phases of said coupling.
The presence of a safety valve and the described positioning of the seal avoid that the seal gets exposed to dangerous stress deriving from possible high differences under pressure between the two elements, because the passage of fluid through the fitting is allow ed only when the seal is certainly covered and protected by the bush even if the bush temporarily backs for the effect of the high pressure difference. Therefore, the seal remains in its seating and carries out correctly its leak tightness function even in particular coupling conditions, when the male element is under pressure and the female element is exhaust, without any occurrence of blow-by and fluid leakage from the fitting.
In addition such a fitting, operating at high pressure does not consent a manual coupling manoeuvre, since the effort to overcome in order to obtain the coupling between the two elements of the fitting is actually above normal human capacity.
In view of this, object of the present invention is to implement a pipe fitting with a safety valve, which allows the manual coupling of the two elements of the fitting even in case of high operating pressure.
According to the invention such aim has been achieved with a fitting comprising a female element and a male element couplable to each other, which elements are made of fixed parts and axially sliding parts that, when at rest, are arranged in a closing position of a passage for opening for fluid and in the occurrence of the coupling between the two elements are displaced by their engagement with corresponding parts of the other element to a position of opening of said passage opening, said fixed parts of the female element comprising a valve element consisting of a fixed axial internal shaft with an enlarged end and said sliding parts of the female element comprising an axially sliding bush arranged coaxially outside of said shaft in a way as to define an interspace constituting part of said passage opening for the fluid and stressed elastically to engage with said enlarged end of the shaft in order to close tight said interspace with respect to the passage of fluid in absence of coupling with the male element, said fixed parts of the male element comprising a fixed body provided with a seal coverable with said bush of the female element in the occurrence of said coupling and said sliding parts of the male element comprising a sliding piston stressed elastically to a position of lateral engagement with said seal in order to close tight an axial cavity of the male element that constitutes an additional part of said passage opening for fluid and to open it after its frontal engagement with said enlarged end of the shaft of the female element in the occurrence of the coupling of the two elements of the fitting, and a safety valve located between said axial cavity of the male element and an end of the male element connectable to a fluid feed in order to lock the communication between said feed and said axial cavity and actuated by said piston in a way as to open said communication after the opening of said interspace of the female element and of said cavity of the male element and substantially at the end of said coupling, characterised in that said male element comprises also a pressure relieve valve interposed between said fluid feed and a pressure relieve chamber and provided with an opening pin arranged in a way as to be actuated directed by said piston just before the opening movement of the safety valve.
In this way, before the opening of the safety valve, there occurs a pressure relieve that allows to carry out the manual coupling of the two elements of the fitting even in presence of a high operating pressure and without any leak of fluid.